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AP Chemistry
8.11 pH and Solubility
8.3 Weak Acid and Base Equilibria
AdvancedMCQMathematicalConceptual14.3k
A student investigates the effect of \(\text{pH}\) on the solubility of three hypothetical sparingly soluble salts: \(\text{MX}\), \(\text{MY}\), and \(\text{MZ}\). Each salt has a \(1:1\) cation-to-anion ratio and dissolves according to the generic equation:

\[ \text{MA(s)} \rightleftharpoons \text{M}^+\text{(aq)} + \text{A}^-\text{(aq)} \]

The student gathers the equilibrium data shown in the table below at \(298\text{ K}\).

Salt\(K_{sp}\) at \(298\text{ K}\)Anion\(pK_b\) of Anion at \(298\text{ K}\)
\(\text{MX}\)\(1.0 \times 10^{-10}\)\(\text{X}^-\)\(4.2\)
\(\text{MY}\)\(1.0 \times 10^{-8}\)\(\text{Y}^-\)\(9.5\)
\(\text{MZ}\)\(1.0 \times 10^{-6}\)\(\text{Z}^-\)\(16.2\)

Equal volumes of saturated solutions of each salt (each in contact with excess solid) are treated with a strong acid to lower the \(\text{pH}\) from \(7.0\) to \(2.0\). Which of the following correctly ranks the salts from greatest to least increase in molar solubility upon acidification, and provides the correct justification?

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